Construction Panel Having Improved Fixing Strength

ABSTRACT

A plasterboard comprises a gypsum matrix having a polymeric additive distributed therein in an amount of at least 1 wt % relative to the gypsum, the gypsum matrix further having a first group of fibres and a second group of fibres embedded therein, wherein the fibres of the first group of fibres have an average length that is at least three times the average length of the fibres of the second group of fibres.

FIELD OF THE INVENTION

The present invention relates to panels for use in buildingconstruction. In particular, the present invention relates to panels forproviding partitions to which items such as sinks, televisions, orradiators may be affixed.

BACKGROUND TO THE INVENTION

Light-weight panels such as plasterboard (e.g. gypsum plasterboard),polystyrene board and fibreboard are commonly used to provide partitionswithin buildings. Their advantages for this application include the factthat they are light and quick to install.

However, in certain cases, such light-weight panels may have thedrawback that they are not strong enough to support fixtures (e.g.sinks, televisions, radiators, fire extinguishers, shelves and any otheritem that requires attachment to the panel). In such cases, the weightof the fixture may cause the fixing means (e.g. screws) to be pulled outof the panel, such that the fixture falls away from the partition.

Typically, this problem has been addressed by providing plywood sheetsto increase the fixing strength of the panel. In this case, the plywoodsheet is provided on the side of the panel opposite to that on which thefixture is to be located. The plywood sheet may provide increasedstrength for retaining one or more fixing means (e.g. screws) employedto secure the fixture to the panel. Typically, the plywood sheet ispositioned within the partition framework, and the plasterboard thenfixed to the plywood, so that it lies outside the partition framework.

As an alternative, metal support means may be provided. These maycomprise fixing plates, channels, straps, or metal fasteners. As is thecase for plywood sheets, the metal support means are generallypositioned on the side of the panel opposite that to which the fixtureis to be secured, and act to receive and secure fixing means, e.g.fixing screws, that are used to attach the fixture to the panel.

Both these arrangements have the disadvantage that they require thepanels and the additional supporting components to be affixed to eachother on-site. Moreover, when metal support means are used, a pluralityof such support means may be needed to support the full set of fixingmeans required to secure the fixture to the panel. Thus, theinstallation process may be time-consuming and expensive.

Furthermore, the addition of metal support means or plywood sheetsincreases the weight and thickness of the partition, and/or results in areduction in cavity wall space. In general, the plywood itself must becut to size on site, thus increasing the time required for installationand possibly leading to the release of dust and potentially harmfulcomponents.

Therefore, there is a need to provide improved panels that are able toretain fixing means and support fixtures, and that do not requiretime-consuming installation processes.

SUMMARY OF THE INVENTION

It has been found that by including a mixture of fibres in theplasterboard, an improvement in the ability of the panel to retainfixing means may be achieved. This may allow stronger plasterboards tobe produced, or lighter plasterboards having acceptable strength.

It has also been observed that by using a mixture of fibres, theviscosity of stucco slurry may be decreased, thereby allowing for easiermanufacture of the plasterboard.

Therefore in a first aspect, the present invention may provide aplasterboard comprising a gypsum matrix having a polymeric additivedistributed therein in an amount of at least 1 wt % relative to thegypsum, the gypsum matrix further having a first group of fibres and asecond group of fibres embedded therein, wherein the fibres of the firstgroup of fibres have an average length that is at least three times theaverage length of the fibres of the second group of fibres.

Preferably, the fibres of the first group of fibres have an averagelength that is at least four times the average length of the fibres ofthe second group of fibres.

By including shorter fibres in addition to longer fibres, it may bepossible to increase the strength of the plasterboard, while avoidingincreases in the viscosity of the stucco slurry used to produce theboard. Excessive viscosity of the slurry tends to be linked to theformation of voids and/or the need to reduce line speeds duringproduction in order to avoid this.

The first group of fibres may comprise inorganic fibres, such as glassfibres. The glass fibres typically have an average length greater than 1mm, preferably greater than 2 mm, most preferably greater than 3 mm. Ingeneral, the glass fibres have an average length less than 10 mm,preferably less than 8 mm.

Preferably, the glass fibres are coated with a sizing agent to increasetheir affinity to gypsum, as is known in the art.

The second group of fibres may comprise organic fibres, such ascellulose-based fibres (for example, cellulose fibres or wood fibres).The cellulose-based fibres typically have an average length greater than100 μm, preferably greater than 200 μm. In general, the cellulose-basedfibres have an average length less than 1.8 mm, preferably less than 1mm, most preferably less than 800 μm. In general, the thickness of thecellulose-based fibres is greater than 10 μm, preferably greater than 20μm. Typically, the thickness of the cellulose-based fibres is less than60 μm, preferably less than 40 μm.

The apparent density of the cellulose-based fibres before incorporationinto the gypsum product is typically less than 250 g/L.

In other embodiments, the organic fibres may be e.g. polyethylene,polypropylene, or polyester fibres.

Typically, the fibres of the first group of fibres have an averagelength that is greater than 1 mm, preferably greater than 2 mm, mostpreferably greater than 3 mm. In general, the fibres of the first groupof fibres have an average length that is less than 10 mm, preferablyless than 8 mm.

The fibres of the second group of fibres typically have an averagelength greater than 100 μm, preferably greater than 200 μm. In general,the fibres of the second group of fibres have an average length lessthan 1.8 mm, preferably less than 1 mm, more preferably less than 800μm.

In general, the thickness of the fibres of the second group of fibres isgreater than 10 μm, preferably greater than 20 μm. Typically, thethickness of the fibres of the second group of fibres is less than 60μm, preferably less than 40 μm.

In general, the first and second groups of fibres are present in a totalamount that is less than 20 wt % relative to the gypsum matrix,preferably less than 15 wt %, more preferably less than 10 wt %.

Preferably, the polymeric additive is distributed in the gypsum matrixin an amount of at least 2 wt %, most preferably at least 3 wt %.

Typically, the polymeric additive is a starch. Preferably, the polymericadditive is present in an amount of less than 20 wt % relative to thegypsum matrix, preferably less than 15 wt %.

In certain embodiments of the first aspect of the invention, theplasterboard has paper facings. These paper facings may comprise bothcellulose fibres and glass fibres, as this is thought to improve thefire resistance of the plasterboard. In other cases, the plasterboardmay have a mat partially or fully embedded at its surface, for example,a glass mat.

In certain embodiments of the first aspect of the invention, the gypsummatrix comprises a hydrophobic additive, such as silicone oil or wax.

In certain embodiments of the first aspect of the invention, the gypsummatrix may contain a biocide.

In certain embodiments of the first aspect of the invention, the gypsummatrix may contain an anti-shrinkage agent such as unexpandedvermiculite, microsilica, and/or clay, in order to improve thefire-resistance of the product.

Certain embodiments of the first aspect of the invention may includefoam or lightweight aggregate such as perlite. Such additives are knownin the art to produce lower-density boards having acceptable thickness.

DETAILED DESCRIPTION

The invention will now be described by way of example only.

Gypsum plasterboards were prepared using the following generalmethodology:

Stucco and other dry additives were weighed into a bag and shaken to mixthem. Water and wet additives were weighed into a bowl. The fibres wereweighed, added to the wet additives in the bowl, and mixed togetherusing an electric mixer for 30 s.

The dry powdered additives were added to the wet additives in the bowland mixed in with the electric mixer for 30 s.

The resultant slurry was sandwiched between two sheets of boardlinepaper and allowed to hydrate for 25 minutes measured from the time ofmixing. The board was then dried in an oven for 50 minutes at 180° C.with a relative humidity greater than 80%.

Example 1

A gypsum plasterboard was prepared from the following ingredients:

-   -   stucco;    -   ethylated starch in an amount of 5 wt % relative to the amount        of stucco (the starch is available from Grain Processing        Corporation under the trade name Coatmaster K57F);    -   glass fibre in an amount of 5 wt % relative to the amount of        stucco. The glass fibres had an average length of 6 mm;    -   cellulose fibre in an amount of 2 wt % relative to the amount of        stucco. The cellulose fibres had an average length of 500 micron        and an average diameter of 35 micron.

Example 2

A gypsum plasterboard was prepared from the following ingredients:

-   -   stucco;    -   ethylated starch in an amount of 10 wt % relative to the amount        of stucco (the starch is available from Grain Processing        Corporation under the trade name Coatmaster K57F);    -   glass fibre in an amount of 5 wt % relative to the amount of        stucco. The glass fibres had an average length of 6 mm;    -   cellulose fibre in an amount of 5 wt % relative to the amount of        stucco. The cellulose fibres had an average length of 500 micron        and an average diameter of 35 micron.

Comparative Example 1

A gypsum plasterboard was prepared from the following ingredients:

-   -   stucco;    -   ethylated starch in an amount of 5 wt % relative to the amount        of stucco (the starch is available from Grain Processing        Corporation under the trade name Coatmaster K57F);    -   glass fibre in an amount of 5 wt % relative to the amount of        stucco. The glass fibres had an average length of 6 mm.

Comparative Example 2

A gypsum plasterboard was prepared from the following ingredients:

-   -   stucco;    -   ethylated starch in an amount of 10 wt % relative to the amount        of stucco (the starch is available from Grain Processing        Corporation under the trade name Coatmaster K57F);    -   glass fibre in an amount of 5 wt % relative to the amount of        stucco. The glass fibres had an average length of 6 mm.

Comparative Example 3

A gypsum plasterboard was prepared from the following ingredients:

-   -   stucco;    -   starch in an amount of 6 wt % relative to the amount of stucco        (the starch is available from Tate & Lyle under the trade name        Merifilm);    -   glass fibre in an amount of 2 wt % relative to the amount of        stucco. The glass fibres had an average length of 6 mm.

Comparative Example 4

A gypsum plasterboard was prepared from the following ingredients:

-   -   stucco;    -   starch in an amount of 6 wt % relative to the amount of stucco        (the starch is available from Tate & Lyle under the trade name        Merifilm);    -   glass fibre in an amount of 1 wt % relative to the amount of        stucco. The glass fibres had an average length of 6 mm;    -   polypropylene fibre in an amount of 1 wt % relative to the        amount of stucco. The polypropylene fibres had an average length        of 6 mm.

Screw Pull-Out Strength

Screw pull-out tests were carried out on samples measuring 100 mm by 100mm that had been conditioned at a temperature of 23° C. and a relativehumidity of 50%. A 50 mm single thread wood screw was inserted into thesample, passing through a metal load transfer element positioned on thesurface of the sample. The load transfer element has a first portionthat is configured to lie between the screw head and the surface of thesample, and a second portion that is configured to engage with a testingmachine so as to allow a load to be applied to the screw along the axisof the screw. The screw was tightened to a torque of 1 Nm.

The specimen was then mounted in a Zwick Universal Testing Machine and a10N pre-load applied to the screw along the axis of the screw.Subsequently, the load was increased by setting a constant cross-headspeed of 10 mm/minute until pull out was achieved.

The results are set out in Table 1. These are averages, each taken from8 samples.

TABLE 1 Example Average screw pull-out strength Example 1 494.9Comparative example 1 305.1 Example 2 671.0 Comparative example 2 535.5Comparative example 3 574 Comparative example 4 558

1. A plasterboard comprising a gypsum matrix having a polymeric additivedistributed therein in an amount of at least 1 wt % relative to thegypsum of the gypsum matrix, the gypsum matrix further having a firstgroup of fibres and a second group of fibres embedded therein, whereinthe fibres of the first group of fibres have an average length that isat least three times the average length of the fibres of the secondgroup of fibres.
 2. A plasterboard according to claim 1, wherein thefibres of the first group of fibres have an average length of 2-10 mm.3. A plasterboard according to claim 1, wherein the first and secondgroups of fibres are present in a total amount that is less than 20 wt %relative to the gypsum matrix.
 4. A plasterboard according to claim 1,wherein the first group of fibres comprises glass fibres.
 5. Aplasterboard according to claim 1, wherein the second group of fibrescomprises cellulose-based fibres.
 6. A plasterboard according to claim5, wherein the cellulose-based fibres have a length of 200 micron to 1.8mm.
 7. A plasterboard according to claim 5, wherein the cellulose-basedfibres have a thickness of 20-60 micron.
 8. A plasterboard according toclaim 1, wherein the polymeric additive is starch.
 9. A plasterboardaccording to claim 1, wherein the polymeric additive is present in anamount of less than 20 wt % relative the gypsum matrix.
 10. Aplasterboard comprising: a gypsum matrix; a polymeric additive withinthe gypsum matrix in an amount of at least 1 wt % relative to the gypsumof the gypsum matrix; cellulose-based fibres within the gypsum matrix;and glass fibres within the gypsum matrix, the glass fibres having anaverage length that is at least three times the average length of thecellulose-based fibres.
 11. The plasterboard of claim 10, wherein theglass fibres have an average length of 2-10 mm.
 12. The plasterboard ofclaim 10, wherein the cellulose-based fibres and glass fibres arepresent in a total amount that is less than 20 wt % relative to thegypsum matrix.
 13. The plasterboard of claim 10, wherein thecellulose-based fibres have a length of 200 micron to 1.8 mm.
 14. Theplasterboard of claim 10, wherein the polymeric additive is present inan amount of less than 20 wt % relative the gypsum matrix.
 15. Theplasterboard of claim 10, wherein the polymeric additive is starch. 16.The plasterboard of claim 10, wherein the cellulose-based fibres have athickness of 20-60 micron.
 17. The plasterboard of claim 10, wherein:the polymeric additive is starch. the cellulose-based fibres and glassfibres are present in a total amount that is less than 20 wt % relativeto the gypsum matrix.
 18. The plasterboard of claim 10, wherein: thepolymeric additive is present in an amount of less than 20 wt % relativethe gypsum matrix; the glass fibres have an average length of 2-10 mm;and the cellulose-based fibres have an average length of 200 micron to1.8 mm.